Video systems, which are used to make images stereoscopically perceived, recently become popular. A video system typically includes a display device, which displays stereoscopic images, and an eyewear device, which assists in viewing the images (e.g. Patent Documents 1 and 2). The display device alternately displays a left frame image, which is observed with the left eye, and a right frame image, which is observed with the right eye. The eyewear device includes liquid crystal shutters which open and close in synchronization with display switching operation between the left and right frame images. The liquid crystal shutter situated in front of the left eye opens while the left frame image is displayed, and closes while the right frame image is displayed. A liquid crystal shutter situated in front of the right eye closes while the left frame image is displayed, and opens while the right frame image is displayed. The left and right frame images are different in contents by an amount of parallax. As a result of the aforementioned synchronization operation of the liquid crystal shutters, a viewer recognizes the parallax between the left and right frame images to stereoscopically perceive the displayed images on the display device.
The synchronization between the display device and the eyewear device is controlled by means of infrared rays or radio signals. Since the eyewear device is not physically connected to the display device, a viewer may watch images at a desired position.
An appropriate communication between the display device and the eyewear device is important for the synchronization operation of the liquid crystal shutters with the image display. However, the eyewear device may not sometimes appropriately receive a signal transmitted from the display device. For example, if the viewer looks aside from the display device, it becomes likely that the eyewear device fails to receive signals from the display device. The eyewear device may also malfunction under influence from noise signals.
In order to overcome the unreliable communication between the display device and the eyewear device, various eyewear devices, which operate in a flywheel mode on the basis of control data extracted from appropriately received signals, have been proposed. Even without signals appropriately received from the display device (non-reception period), these eyewear devices operate on the basis of the control data obtained before the non-receiving period. Therefore, a viewer may appropriately continue watching displayed images on the display device.
The operation of the liquid crystal shutters on the basis of the control data obtained in advance is also helpful to prevent noise signals from causing a malfunction in the eyewear device. For example, if a switching timing of the liquid crystal shutters is considerably different between control data obtained in advance and newly obtained control data, the eyewear device may determine that the new control data are generated from noise signals.
A change in image display operation (display mode) of the display device may require a change in the synchronization operation of the liquid crystal shutters. For example, if a video frame rate is changed, the synchronization operation of the liquid crystal shutters has to become a coincident operation frequency with the frame rate after the change. Or if a viewer changes a channel of the display device (e.g. a TV device), a phase of the cyclic display operation of the display device may change. In this case, the liquid crystal shutters have to perform the opening and closing operation under the new phase.
As described above, in many cases, the eyewear device uses the control data obtained in advance to open and close the liquid crystal shutters. However, it is difficult to instantaneously switch the video frame rate in the display device. Therefore, the video synchronization signal of the display device is disrupted while the frame rate is shifted to a new one (e.g. several seconds at the longest). Therefore, if the control data of the liquid crystal shutters are directly output in response to the video synchronization signal, the opening and closing operation of the liquid crystal shutters is disrupted as well. As described above, the operation of the liquid crystal shutters is influenced by the control data obtained in advance. Therefore, it is difficult to immediately switch the frame rate to the new frame rate. For example, if a display mode, in which left and right frame images are displayed at 60 Hz, respectively, is switched to another display mode, in which left and right frame images are displayed at 48 Hz, respectively, the opening and closing operation of the liquid crystal shutters is not instantaneously switched to the 48 Hz display mode. During the transition, the liquid crystal shutters irregularly open and close.
If there is a change in an image adjustment mode (e.g. image quality mode of TV) of the display device, it may be necessary not only to adjust the image quality in response to images, but also to change the opening and closing timings of the liquid crystal shutters. In this case, it is also difficult to instantaneously change the control data from the display device. Therefore, the opening and closing operation of the liquid crystal shutters is disrupted during the transition to the new control data.
In some cases, a flywheel mode is provided to allow a continuous operation of the eyewear device for a while at a timing determined by the previously detected control data, even if the control data from the display device is momentarily interrupted by impediments. However, the flywheel of the eyewear device may cause a flicker because of an unsynchronized opening and closing operation of the liquid crystal shutters at the previously determined timing with images although the timing of the shutters should have been changed in coincidence with the change in the display mode.
Due to the aforementioned reasons, unsynchronized or irregular opening and closing operation of the eyewear device may make a viewer perceive a flicker under the disturbed opening and closing operation of the liquid crystal shutters or the interfered synchronization of the liquid crystal shutter with images. This may irritate the viewer.
The flicker may occur under the following switching operation of the display mode. For example, if the display device is designed not only to display stereoscopic images (stereoscopic display mode), but also to alternately display two different programs (first program and second program: dual display mode), a few viewers may selectively view the first and second programs. If one of the viewers watches the first program, the liquid crystal shutters of the eyewear device worn by the viewer open while the first program is displayed, and close while the second program is displayed. The liquid crystal shutters of the eyewear device worn by another viewer may close during the display of the first program and open while the second program is displayed. A switching operation of the display mode of the display device from the stereoscopic display mode to the dual display mode requires a significantly different operation from the synchronized operation during the stereoscopic display mode for the liquid crystal shutters of the eyewear device. However, the eyewear device affected by the control data obtained in advance may not immediately execute the operation for the dual display mode. As a result, the viewers may perceive an unpleasant flicker.    Patent Document 1: JP 11-98538 A    Patent Document 2: JP 2000-36969 A